A test item exhibits differential item functioning (DIF) if students with the same ability find it differentially difficult. When the item is administered in French and English, differences in language difficulty and meaning are the most likely explanations. However, curriculum differences may also contribute to DIF. The responses of Ontario students to Measurement and Geometry items from the content subtest of the 2001 School Achievement Indicators Program Mathematics Assessment were analyzed using item response theory-based procedures. DIF between the French and English versions was investigated. Attempts to interpret the DIF found in terms of translation and curriculum influences were partially successful. Alternative explanations and suggestions for additional research are provided.